Time proportioning electrical control device

ABSTRACT

An electrical control device designed to produce a variable electrical signal proportional to the degree of change of an environmental parameter over a preselected band width. A pair of electrical contacts in a normally spaced apart relation are connected in series between a signal source and the element to be controlled so that the signal is allowed to be transmitted to the element upon the closing of the contacts. This invention operates by using a high frequency interruption of a signal current by means of a pair of opening and closing contacts. One contact is positioned relative to the other by means of an environmental sensing device responding to changes in a particular environmental parameter. The second contact is mechanically coupled to the current responsive device for effecting movement of the second contact away from the first contact when energized to provide a continuous interruption of the signal, where the ratio of the current responsive device&#39;&#39;s on-time to off-time is proportional to the degree of change of the environmental parameter within the preselected band width.

United States Patent Emmons [54] TIME PROPORTIONING ELECTRICAL CONTROLDEVICE [72] Inventor: Robert Eugene Emmons, Goshen,

Ind.

[73] Assignee: Penn Controls, Inc., Oak Brook, Ill.

[22] Filed: May 6, 1971 211 Appl. No.: 140,883

[52] US. Cl .l ..337/l24, 337/38 [51] Int. Cl. ..H0lh 71/22 [58] Fieldof Search ..337/38, 99, 101, 123, 124, 337/299, 300, 378

[56] References Cited UNITED STATES PATENTS 2,817,741 l2/l957 Turner..337/99 X 2,852,640 9/1958 Lancey ..337/99 X 2,908,786 10/1959Schleicher ..337/l0l Primary Examiner-Bernard A. GilheanyAssistant'Examiner-F. E. Bell Attorney-Johnson, Dienner, Emrich, Verbeck& Wagner [451 Sept. 26, 1972 [57] ABSTRACT An electrical control devicedesigned to produce a variable electrical signal proportional to thedegree of change of an environmental parameter over a preselected bandwidth. A pair of electrical contacts in a normally spaced apart relationare connected in series between a signal source and the element to becontrolled so that the signal is allowed to be transmitted to theelement upon the closing of the contacts. This invention operates byusing a high frequency interruption of a signal current by means of apair of opening and closing contacts. One contact is positioned relativeto the other by means of an environmental sensing device responding tochanges in a particular environmental parameter. The second contact ismechanically coupled to the current responsive device for effectingmovement of the second contact away from the first contact whenenergized to provide a continuous interruption of the signal, where theratio of the current responsive device's on-time to off-time isproportional to the degree of change of the environmental parameterwithin the preselected band width.

10 Claims, 9 Drawing Figures PATENTEDsms m2 3 694, 78 7 SHEET 1 0F 2fnz/enfovt I Roberi Z1 15987262 7227720725, 5?; WW @WJM M Q MW 2.

BACKGROUND OF THE INVENTION This invention relates to an electricalcontroldevice for providing a signal proportional to the degree ofchange of an environmental parameter and in particular relates to thetype of electrical control devices that operate by a high frequencyinterruption of the signal current effected by a rapid make and break ofa pair of contacts.

This invention answers the need for a reliable and economical means ofproviding a proportional signal current of sufficient magnitude tooperate a variety of different primary controls such as valve operators,damper motors, and staging switches.

SUMMARY OF THE INVENTION This invention relates to an electrical controldevice for providing a variable electrical signal proportional to thedegree of change of a particular environmental parameter over apreselected band width. The invention employs a pair of electricalcontacts disposed in a normally spaced apart relation and adapted to beconnected in series between a signal source and the element to becontrolled such that the signal current is permitted to pass to theelement when the electrical contacts are closed together. A sensordevice responsive to variations of the particular environmentalparameter being detected functions to proportionally move an actuatormember. This actuator member is disposed such that it moves a firstcontact into engagement with the second contact whenever theenvironmental parameter is within the preselected band width. Uponclosing the contacts, acurrent responsive device is energized causingthe second contact to move away from the first contact to interrupt thesignal. A continuous interruption of the signal is affected by thecurrent responsive device by using the dimensional extension of anelectrical conductor wire due to the heat generated by the signalcurrent passing through the wire. By using an electrical conductivewire, it is possible to adjust the ratio of the on-time to off-time ofthe current responsive device to be proportional to the degree of changeof the environmental parameter of the preselected band width.

. BRIEF DESCRIPTION OF DRAWINGS For a better understanding of thisinvention, reference may be had to the accompanying drawings in which:

FIG. 1 is a schematic view of one embodiment of this invention;

FIG. 2 is a schematic view of a second embodiment of this invention;

FIG. 3 is a schematic view of a third embodiment of this invention;

FIG. 4 is a schematic view of a fourth embodiment of this invention;

FIG. 5 is a schematic view of a fifth embodiment of this invention;

FIG. 6 is a schematic view of a sixth embodiment of this invention;

FIG. 7 is a seventh embodiment of this invention showing the use of theinvention is a proportional thermostat;

FIG. 8 is an enlarged partial view of FIG. 7; and FIG. 9 is a frontperspective view of the cantilever means used in the embodiment of FIG.7.

FIRST EMBODIMENT There is shown in FIG. 1, the first embodiment of myinvention in the form of a thermostat 10 represented schematically andhaving first and second electrical contacts 12 and 14. First contact 12is positioned relative to second contact 14 by a conventional bimetalelement 16 responding to the surrounding temperature. Second contact 14is mounted on the outer end of a spring leaf 18, which biases contact 14away from con tact l2.

Thermostat 10 is designed to operate by means of a high frequencyinterruption of the signal current passing through the contacts 12 and14 by virtue of a continuous making and breaking of contacts. Thisdesired interruption is effected by means of a current responsive device20 mechanically displacing second contact 14 away from first contact 12.The current responsive device 20 uses an electrical conductive wire inthe form of a length of fine wire 22 to cause this displacement bypassing the signal current through the wire upon closure of the contactsto heat the wire until its length increasesby a sufficient amount tobpen the contacts. Upon cooling, the wire 22 contracts to again closethe contacts and this action is repeated until the first contact 12 isrepositioned by the bimetal element 16 away from second contact 14.

The dimensional excursion of the electrical conductive wire 22 is usedin the FIG. 1 embodiment to open the contacts by mounting the left end24 of the wire 22 to a fixed position and mounting the right end 26 tothe spring leaf 18 such that the wire 22 is in a perpendicularrelationship to the spring leaf. The spring leaf 18 biases the contact12 towards the right,and the extension of the length of wire 22 willpermit the contact 14 to move towards the right until its engagementwith contact 12 is broken. The material of the wire 22 and itscross-section must be chosen with regard to the density of the signalcurrent to provide sufficient heating to effect the necessarydimensional change of length. The total length of the wire 22 must beselected to correlate the movement of the first contact 12 by thebimetal element 16 in order to provide sufficient expansion to actuatethe second contact 14 over a preselected temperature band. The phrasepreselected temperature band is intended to mean the amount of change intemperature from a desired room temperature, hereinafter called the OFFtemperature for thermostat 10.

To explain the operation of the first embodiment, an example will begiven. Assume a fine stainless steel wire is used for the conductor 22having characteristics that the amperage of the signal current increasesits temperature by F above ambient, and that at this temperature thelength of the wire increases by 4 mils. The bimetal 16 is then selectedso that it will change the position of contact 12 by 4 mils in responseto a change of 4 F in the ambient temperature from the OFF temperature.The thermostat condition could then change from contacts being fullyclosed to fully open with a room temperature change of 4 F and would besaid to have a band width of 4 degrees. If then the room temperaturechanges 1 degree below the OFF temperature,

the contacts 12 and 14 will be on one-fourth of the time and offthree-fourths of the time since the contact 14 must only be moved 1 milto open the contacts. If the room temperature should suddenly change 3degrees below the OFF temperature, the contacts 12 and 14 would then beon three-fourths of the time and off onefourth of the time. Thus it canbe seen that the device being controlled is energized for a relativelylong length of time if the variation in temperature from the OFFtemperature is large. Thus, when the room temperature is within theproportional band of the thermostat, the amount of work done will bedirectly related to the percentage of the time that the current flows toprovide a proportional band width.

In the above example, it should be noted that the temperature of thewire never attains 100 degr'ee rise at one-fourth ON time, but morerealistically about 35 degrees or just enough to provide sufficientexpansion to open the contacts. Since the opening and closing of thecontacts occur at a high frequency, the wire does not cool down toambient, but rather the wire temperature oscillates between twotemperatures that provide just enough movement and force differential tomove the contact structure for second contact 14.

The first embodiment schematically illustrated in FIG. 1 embodies theprinciples of this invention to provide a new concept in thermostaticdevices designed for heating or cooling control. This new concept isembraced in the combination of the use of an energized wire foreffecting a precise and predetermined amount of movement to control theeffective width of the proportional band and a separate sensingdevice,such as a bimetal, responding to changes in the ambienttemperature to adjust the relation of on-time to off-time within theproportional band.

SECOND EMBODIMENT There is shown in FIG. 2 a second embodiment of thisinvention comprising a thermostat 30 designed to operate with a highfrequency interruption of the signal current. This embodiment operatesin the same manner as the first embodiment but is designed to cover ashort .temperature range by using a conventional bimetal helix 32 forchanging the position of the first contact 34. The second contact 36 issecured to the outer end of a contact leaf 38 and is spring-biasedtowards the right by virtue of a separate spring 40. The currentresponsive device 42 for the second embodiment is identica to that shownin the first embodiment comprising a length of conductive wire 44 havingits left end 46 mounted in a fixed position and its right end 48fastened to the contact leaf 38. One difierence in the second embodimentfrom the first embodiment is that the signal current bypasses thebimetal 32 by the addition of a spring member 50 fastened adjacentcontact 34, where the device to be controlled is electrically connectedto its outer terminal 52.

. THIRD EMBODIMENT Referring to FIG. 3, the thermostat 54 illustrates analternative means of mechanically interconnecting the thermal responsiveelectrical conductive wire 56 to the second contact 58 by using anelongated linking member 60 stretched between the approximate midpointof the wire 56 and the contact leaf 64 adjacent the second contact 58.By virtue of this arrangement, it is possible to amplify the linealextension of the wire 56 to move the second contact 58 by a factor oftwo or three times the lineal extension of the wire 56. This of coursepermits a much shorter length of thermal responsive wire 56 to be usedin the thermostat, which is an important advantage in the design ofthermostats where space limitations are always critical. An insulator 68interconnects the left end 65 of the linking member 60 to the mid-point62 of the thermal responsive wire 56 to prevent current flow in thelinking member. The right end 66 of linking member 60 is secured tospring contact leaf 64.

The third embodiment shown in FIG. 3 has a first contact 70 positionedrelative to the second contact 58 by a conventional bimetal helix 72.The current path for the signal current when the contacts 58 and 70 areclosed, is through the contact leaf 64 through bimetal helix 72 andthrough the thermal responsive wire 56.

The operation of the third embodiment illustrated in FIG. 3 is identicalto the first and second embodiments, except that the movement of thethermal responsive wire 56 is two or three times less than those of thefirst two embodiments for the same band width since the loading of thethermal responsive wire at right angles to its length permits two orthree times the movement obtainable by the direct extension of wirelengths for the same temperature range.

FOURTH EMBODIMENT The embodiment of FIG. 4 is identical in function andoperation to that of FIG. 3, but its parts are arranged in a somewhatdifferent structural manner.

The first and second electrical contacts and 82 are supported in anormally spaced apart relation from a common terminal block 84 by meansof a pair of contact leafs 86 and 88, respectively. The first contact 80is positioned relative to the second concept 82 by a conventionalbimetal helix 90 responding to the surrounding temperature.

The thermal responsive electrical conductive wire 92 has its oppositeends 94 and 96 mounted in fixed positions and its mid-point 98interconnected to the second contact leaf 88 by means of a linkingmember 100 disposed in approximate 90 degree relationship with thethermal responsive wire 92.

Current flow is prevented from flowing through the linking member 100 byvirtue of an electrical insulator 102. A separate spring 106 is alsoconnected at the midpoint 98 of the thermal responsive wire 92 toprovide separate loading on the wire 92 in a direction to move thesecond contact 82 away from the first contact 80. A separate spring,such as spring 106, may be desirable in addition to the contact leaf 88where a large diameter wire 92 is used to provide increased electricalcurrent.

The path of the signal current through the thermostat 78 is between theterminal 96 and the terminal 108 to permit the signal current to passthrough the thermal responsive wire 92 through contact leaf 88 andthrough the bimetal helix 90.

FIFTH EMBODIMENT The first four described embodiments employ theprinciples of this invention to provide a thermostatic device having aproportional band that uses a thermal responsive wire for a precise andpredeterminable amount of movement to control the effective width of theproportional band. In these embodiments, a temperature sensing device,such as a bimetal, is used to respond to the ambient temperature andthereby adjust the relation of the on-time to off-time within 'theproportional band. As will now be illustrated, the concept oftime-proportioning by using a thermal responsive wire is in no waylimited to being controlled by a temperature responsive device, but maybe actuated by many kinds of sensing devices such as bellows ordiaphragms for pressure sensing, hair or other materials for humiditycontrol, etc.

In FIG. 5, there is shown a pressure responsive device 1 in the form ofbellows which could be either a charged thermal element for temperatureactuation or connected to a pressure system for control. Actuation ofthe bellows 110 positions the first contact 112 relative to the secondcontact 114. A spring 116 opposes the movement of the bellows 110 topermit the setting of an OFF position for the FIG. 5 embodiment.

The second contact 114 is mounted on the end of a contact leaf 118 andits movement away from the first contact 112 is effected by the thermalextension of thermal responsive wire 120 in the same manner as the firsttwo embodiments. The thermal responsive wire has its left end 122secured to a fixed position and its right end secured to the contactleaf 118 adjacent the second contact 114.

Upon the contacts 112, 114 closing, a signal current is passed throughthe thermal responsive wir'e 120 causing its length to increase slightlyand allowing the spring 124 to pull the second contact 114 away from thefirst contact 112 to interrupt the signal current.

The pressure responsive device 110 is designed such that it will changethe position of contact 112 by an even amount for a change in theenvironmental parameter being sensed from a desired OFF position todefine a band width. The dimensional extension of the thermal responsivewire 120 is then chosen to increase in length over this band widthtoselectively adjust the relation of on-time to off-time of the signalcurrent within the proportional band in the same manner as the operationof the first four embodiments.

SIXTH EMBODIMENT Referring to FIG. 6, there is shown the use of anothersensing device, in this case a hair element 130 responsive to thesurrounding humidity conditions. A spring element 132 tensions the leftend of the humidity of the hair element 130 to accurately position thefirst contact 134 relative to the second contact 136 in response tochanges in the surrounding humidity.

The second contact 136 is mechanically in contact with the thermalresponsive electrical conductive wire 138 in exactly the same manner asthe FIG. 5 embodiment. The sensing device used to detect the particularenvironmental parameter, such as the hair element 130 in FIG. 6, has noinfluence on the operation of the thermal resp'onsive wire 138. In FIG.6, when the signal current passes through the wire 138, it lineallyextends until contact 136 under the biasing influence of spring 140interrupts the signal current in exactly the same manner as thepreviously described embodiment.

It will be appreciated from the description of the first six embodimentsthat this invention is in no way limited to being controlled by abimetal element but may be actuated by many kinds of sensing devicessuch as bellows or diaphragms for pressure-sensing, hair or othermaterial for humidity control, etc. The time-proportioning of thethermal responsive wire and the use of the hot wire for providing aprecise and predeterminable amount of movement to control the effectivewidth of the proportional bands in combination with the use of aseparate sensing device to measure a particular environmental parameterand thereby adjust the relation of on-time to off-time within theproportional bands is the heart of this invention. The thermalresponsive wire provides a reliable and economical means of producing aproportional signal of sufficient magnitude to operate numerous primarycontrols such as valve operators, damper motors, staging switches, etc.

SEVENTH EMBODIMENT There is shown in FIG. 7, the seventh embodiment ofmy invention in the form of a thermostat which is assembled in acircular casing 152. First and second contacts 154 and 156 are supportedin a normally spaced-apart relation by means of a pair of spring conractleafs 158 and 160, respectively. The spring leafs 158 and 160 aresecured to a contact mounting bracket 162 (only partially shown), whichis mounted on the rear wall 164 of the circular casing 152. Mountingbracket 162 is supported between a pair of mounting posts 166 carried bythe rear wall 164.

First contact 154 is positioned relative to second contact 156 by virtueof a conventional bimetal assembly 168. The bimetal assembly 168comprises a bracket 170 supported on the rear wall 164 of the casing 152by a mounting post 172 and a bimetal helix element 174 having one end176 fastened to the mounting bracket 170 and the other end 178 bentoutwardly and attached to inner end of actuator lever 180. Referring toFIG. 7, it will be appreciated that the outer end of actuator lever 180engages the first contact 154 as it is moved towards the right. Thefirst and second contacts are closed together with a slight displacementof first contact 154 to the right.

As in the first six embodiments, this embodiment employs a thermalresponsive wire 182 to provide a continuous interruption of the currentsignal by utilizing the dimensional extension of the thermal responsivewire. The thermal responsive wire 182 is mechanically interconnected toa lever 184 that is positioned to engage the second electrical contact156 by means of a novel cantilever means 186. The cantilever means 186permits small dimensional extensions of the thermal responsive wire 182to be substantially amplified based on the cantilever principle.Cantilever means 186 comprises a lever bracket 188 having a mountingportion 190 and a holder portion 192. The mounting portion 190 has anopening 194 for mounting the lever bracket on a mounting post 196extending from the rear wall 164 of the casing 152. The holder portion192 which extends in a generally perpendicular relationship to themounting portion 190 has a pair of opposing inwardly extending flanges198 which frictionally grip the lower end of the lever 184. The lever184 is firmly secured in place on the holder portion 192 by means of arivet 200.

The opposite ends 206 and 208 of the thermal responsive wire 182 arefastened to a pair of mounting brackets 210 and 212, which are fixedlysupported on the rear wall 164 of the casing 152. The mid-point 214 ofthe thermal responsive wire 182 is inserted through opening 215 in theholder portion 192 and soldered to the lower end of lever 184 such thatthe mid-point 214 is equidistant from the opposite ends 206 and 208.

The lever bracket 188 is made from an elastic material, such as aberyllium copper alloy, to provide a constant tension force on thermalresponsive wire 182. The mid-point 214 is secured to the holder portion192 after the holder portion 192 is bent counterclockwise about thehinge or pivot point 220 to place it in a state of tension.Consequently, as the thermal responsive wire 182 is heated to expand,the holder portion 192 pivots clockwise about pivot 220 and the outerend of lever 114 swings to the right. Since the distance between thepivot point 220 and the mid-point 214 is relatively short as comparedwith the distance between the pivot point 220 and the outer end of lever184, a

slight extension of the thermal responsive wire 182 will cause arelatively large movement of the second contact. 156 as it follows thedisplacement of lever 184 to the right.

The thermostat depicted in FIG. 7 operates on the same principle as theFIG. 1 embodiment, where the thermal responsive wire 182 provides aprecise and predetermined amount of movement to control the effectivewidth of the proportional band and the temperature sensing deviceresponds to changes in the ambient temperature to adjust the relation ofon-time to off-time within the proportional band. However, the mountingand connecting arrangement of the thermal responsive wire provides anumber of advantages over the mounting arrangement of FIG. 1. One ofthese advantages is that the two half portions of thermal responsiveelement 182 are mechanically in parallel to double its mechanicalstrength. Another advantage is that the cantilever means 186 permitsamplification of the lineal extensions of the thermal responsive wire182 by a factor of two or three times. Consequently, the loss due to theelastic modulus of the wire is much less by virtue of the amplificationto provide a more reliable and more active high frequency contactor. Athermostat constructed as illustrated in FIG. 7 has a very smoothproportioning control throughout its band width.

When the casing 152 for the thermostat 150 is enclosed by a front cover,the heat from the thermal responsive wire 182 produces a secondaryeffect on the bimetal helix 174. This self-heating within the thermostatcan be beneficial to its purpose by apparent widening of theproportioning band when the temperature sensor is designed to open thecontacts on increasing temperature. By reversing the sensor action, awide proportion band could be narrowed if that were desirable.

A thermostat designed to utilize the apparent widening of the band isalso inherently anticipating a change. An example of the heating modeapplication is illustrated by the lowering of the room temperature andclosing of the contacts by the bimetal sensor. Upon closure, the outputsignal demands heat which may require a considerable period of time toreach the thermostat (transport time). Heat is immediately generated inthe thermal responsive wire and accumulates within the enclosureaffecting the bimetal which then "anticipates an increase in temperatureof the room and shortens the amount of time of the passage of signalturns. In other words, the thermostat is time proportioning withanticipation. This can be a stabilizing characteristic of the system ifthe design provides just the right amount of anticipation to correct thesignal and not over-anticipation to create significant droop.

The same thermostat may be used for the cooling mode with anticipation,and will operate in the limits of the same temperature band through acomplete inversion of the output signal or a change of the actuatingcontrol to provide a reversal of attitude between the signal and thecooling equipment. It should be noted that a change in thermostat, suchas reversal of the bimetal action or contact action to reverse its modeof operation, will not provide anticipation. In fact, the heat generatedby the hot wire must be well isolated or it would tend to lock on withthe result of having a wide differential.

It will be apparent from the foregoing that the use of one thermostatdesign for both heating and cooling modes of operation provides greatversatility by using the same components with accessory items added onlywhen required. Also in this system, the proportional band may be widenedas desired by shunting the signal load to increase the current densityin the thermal responsive wire. This being a temperature-currentrelationship, approximately a 50 percent increase in current will doublethe temperature span of the proportioning band. With the suggestedactuator design, this shunting may be done individually on the heatingor cooling terminals. The total amount of anticipation availableincreases with the widening of the proportioning band and thereforeneeds no further consideration except for the value built into theoriginal design.

It will be further apparent that modifications and variations may bemade in the control device of each of the seven embodiments withoutdeparting from the scope of the novel concepts of the present invention.It is accordingly our intention that the scope of the invention belimited solely by that of the hereinafter appended claims.

I claim:

1. An electrical control device for providing a variable electricalsignal proportional to the degree of change of an environmentalparameter over a preselected band width comprising a pair of electricalcontacts disposed in a normally spaced apart relation and adapted to beconnected in series between a signal source and the element to becontrolled to transmit a signal to said element when closed together,sensor means responsive to variations of said environmental parameter toproportionally move an actuator member such that one of said contacts ismoved by said actuator member into engagement with the other of saidcontacts whenever said environmental parameter is within saidpreselected band width, and current responsive means energized by theclosing of said contacts for effecting movement of said other contactaway from said one contact until spaced apart to provide a continuousinterruption of the signal, where the ratio of said current responsivemeans on-time to off-time is proportional to the degree of change ofsaid environmental parameter over said preselected band width saidcurrent responsive means including a length of electrical conductivewire which carries an energizing current upon the closing of saidcontacts and amplification means for moving said other contact by anamplification factor several times the dimensional extension of saidwire, where the heat generated by an energizing current passing throughsaid wire causes the dimensional extension of said wire.

2. An electrical control device as defined in claim 1, wherein saidsensor means comprises a bimetal element responsive to the surroundingtemperature.-

3. An electrical control device for providing a variable electricalsignal proportional to the degree of change of an environmentalparameter over a preselected band width comprising a pair of electricalcontacts disposed in a normally spaced apart relation and adapted to beconnected in series between a signal source and the element to becontrolled to transmit a signal to said element when closed together,sensor means responsive to variations of said environmental parameter toproportionally move an actuator member such that one of said contacts ismoved by said actuator member into engagement with the other of saidcontacts whenever said environmental parameter is within saidpreselected band width, and current responsive means energized by theclosing of said contacts for effecting movement of said other contactaway from said one contact until spaced apart to provide a continuousinterruption of the signal, where the ratio 'of said current responsivemeans on-time to off-time is proportional to the degree of change ofsaid environmental parameter over said preselected band width and wherethe closing of said contacts enables an energizing current to betransmitted through said current responsive means, said currentresponsive means including a length of electrical conductive wire andmeans for connecting said wire to said other contact such thatdimensional extension of said wire in response to the heat generated byan energizing current passing through said wire moves said other contactaway from said one contact until said contacts open throughout said bandwidth, said connecting means including spring means to constantly urgesaid other contact to move away from said one contact.

4. An electrical control device as defined in claim 3, wherein saidmeans for connecting said wire to said other contact comprises anelongated linking member secured between said other contact and theapproximate mid-point of said conductive wire having its opposite endsheld in stationary positions and having said linking member disposed ina substantially perpendicular relation with said wire.

5. An electrical control device as defined in claim 4, wherein saidlinking member is thermally insulated from said conductive wire.

6. An electrical control device for providing a variable electricalsignal proportional to the degree of change of the surroundingtemperature over a preselected band width comprising a pair ofelectrical contacts disposed in a normally spaced apart relation 1. andadapted to be connected in series between a signal source and theelement to be controlled to transmit a signal to said element whentogether, temperature sensor means responsive to variations of thesurrounding temperature 0 proportionally move an actuator member suchthat one of said contacts is moved by said actuator member intoengagement with the other of said contacts whenever the temperature iswithin said preselected band width, and current responsive meansenergized by the closing of said contacts for effecting movement of saidother contact away from said one contact until spaced apart to provide acontinuous interruption of the signal, where the closing of saidcontacts enables an energizing current to be transmitted through saidcurrent responsive means and said current responsive means includes alength of electrical conductive wire and means for connecting said wireto said other contact such that dimensional extension of said wire inresponse to the heat generated by the energizing current passing throughsaid wire moves said other contact away from said one contact until saidcontacts open through said band width, said connecting means includingspring means to constantly urge said other contact to move away fromsaid one contact, whereby the ratio'of the on-time of said currentresponsive means to its off-time is proportional to the degree of changeof the surrounding temperature over said preselected band width.

7. An electrical control device as defined in claim 6, wherein saidmeans for connecting said wire to said other contact comprises anelongated linking member secured between said other contact and theapproximate mid-point of said conductive wire having its opposite endsheld in stationary positions and having said linking member disposed ina substantially perpendicular relation with said wire.

8. An electrical control device as defined in claim 6, wherein saidlinking member is thermally insulated from said conductive wire.

9. An electrical control device as defined in claim 6, wherein saidmeans for connecting said wire to said other contact comprises a leverpivotally mounted to provide a shorter length portion and a longerlength portion, the outer end of said longer length portion beingdisposed to engage said other contact, spring means to urge said othercontact and said outer end of said longer portion to move away from saidone contact and said conductive wire being secured between a fixed pointand the outer end of said shorter end portion, whereby small dimensionalexcursions of said conductive wire cause said other contact to move arelatively large distance in direct proportion to the ratio of thelongitudinal dimensions of said shorter length portion to said longerlength portion.

10. An electrical control device as defined in claim 9, wherein the endsof said conductive wire are fixedly mounted in juxtaposition and theapproximate midpoint of said wire is secured to said outer end of theshorter length portion and is located equidistant from said ends of saidconductive wire.

. UNIT D STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,694,787 7 Dated September 26 1972 Inventor (s) Robe rt g ne Emmons Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

On the title page, line 5, "Penn Controls Inc. Oak Brook,

Illinois" should be Johnson Service Company, Milwaukee,

Wisconsin Signed and sealed this ZZndiday of May 1973.

(SEAL) Attest:

EDWARD'MFLETCHERJR. i v I ROBERT GOTTSCHALK Attesting OfficerCommissioner of Patents FORM PO-1050 (10-69) USCOMNPDC 60376.:69

UNITED STATES PATENT OFFHZE CERTWECATE 0F QQRREQTEQN Patent No. ,7 7 IDated September 26, 1972 Inventor) Robert Eugene Emmons It is certifiedthat error appears in the above-identified patent and that said LettersPatent are herebyeorrected as shown below:

On the title page, line 5 ,"Penn Controls Inc., Oak Brook,

Illinois" should be Johnson Service Company, Milwaukee Wisconsin Signedand sealed this 22nd day of May 1973.

(SEAL) Attest:

ROBERT .GOTTSCHALK EDWARD M.FLETCHER,JR.

Commissioner of Patents Attesting Officer USCOMM-DC 60376-P69 u.s.GOVERNMENT PRINTING OFFICE: I969 0-366-334 F ORM PO-105O (10-69)

1. An electrical control device for providing a variable electricalsignal proportional to the degree of change of an environmentalparameter over a preselected band width comprising a pair of electricalcontacts disposed in a normally spaced apart relation and adapted to beconnected in series between a signal source and the element to becontrolled to transmit a signal to said element when closed together,sensor means responsive to variations of said environmental parameter toproportionally move an actuator member such that one of said contacts ismoved by said actuator member into engagement with the other of saidcontacts whenever said environmental parameter is within saidpreselected band width, and current responsive means energized by theclosing of said contacts for effecting movement of said other contactaway from said one contact until spaced apart to provide a continuousinterruption of the signal, where the ratio of said current responsivemeans on-time to off-time is proportional to the degree of change ofsaid environmental parameter over said preselected band width saidcurrent responsive means including a length of electrical conductivewire which carries an energizing current upon the closing of saidcontacts and amplification means for moving said other contact by anamplificatiOn factor several times the dimensional extension of saidwire, where the heat generated by an energizing current passing throughsaid wire causes the dimensional extension of said wire.
 2. Anelectrical control device as defined in claim 1, wherein said sensormeans comprises a bimetal element responsive to the surroundingtemperature.
 3. An electrical control device for providing a variableelectrical signal proportional to the degree of change of anenvironmental parameter over a preselected band width comprising a pairof electrical contacts disposed in a normally spaced apart relation andadapted to be connected in series between a signal source and theelement to be controlled to transmit a signal to said element whenclosed together, sensor means responsive to variations of saidenvironmental parameter to proportionally move an actuator member suchthat one of said contacts is moved by said actuator member intoengagement with the other of said contacts whenever said environmentalparameter is within said preselected band width, and current responsivemeans energized by the closing of said contacts for effecting movementof said other contact away from said one contact until spaced apart toprovide a continuous interruption of the signal, where the ratio of saidcurrent responsive means on-time to off-time is proportional to thedegree of change of said environmental parameter over said preselectedband width and where the closing of said contacts enables an energizingcurrent to be transmitted through said current responsive means, saidcurrent responsive means including a length of electrical conductivewire and means for connecting said wire to said other contact such thatdimensional extension of said wire in response to the heat generated byan energizing current passing through said wire moves said other contactaway from said one contact until said contacts open throughout said bandwidth, said connecting means including spring means to constantly urgesaid other contact to move away from said one contact.
 4. An electricalcontrol device as defined in claim 3, wherein said means for connectingsaid wire to said other contact comprises an elongated linking membersecured between said other contact and the approximate mid-point of saidconductive wire having its opposite ends held in stationary positionsand having said linking member disposed in a substantially perpendicularrelation with said wire.
 5. An electrical control device as defined inclaim 4, wherein said linking member is thermally insulated from saidconductive wire.
 6. An electrical control device for providing avariable electrical signal proportional to the degree of change of thesurrounding temperature over a preselected band width comprising a pairof electrical contacts disposed in a normally spaced apart relation andadapted to be connected in series between a signal source and theelement to be controlled to transmit a signal to said element whentogether, temperature sensor means responsive to variations of thesurrounding temperature to proportionally move an actuator member suchthat one of said contacts is moved by said actuator member intoengagement with the other of said contacts whenever the temperature iswithin said preselected band width, and current responsive meansenergized by the closing of said contacts for effecting movement of saidother contact away from said one contact until spaced apart to provide acontinuous interruption of the signal, where the closing of saidcontacts enables an energizing current to be transmitted through saidcurrent responsive means and said current responsive means includes alength of electrical conductive wire and means for connecting said wireto said other contact such that dimensional extension of said wire inresponse to the heat generated by the energizing current passing throughsaid wire moves said other contact away from said one contact until saidcontacts open through said band width, said connecting means includingspring mEans to constantly urge said other contact to move away fromsaid one contact, whereby the ratio of the on-time of said currentresponsive means to its off-time is proportional to the degree of changeof the surrounding temperature over said preselected band width.
 7. Anelectrical control device as defined in claim 6, wherein said means forconnecting said wire to said other contact comprises an elongatedlinking member secured between said other contact and the approximatemid-point of said conductive wire having its opposite ends held instationary positions and having said linking member disposed in asubstantially perpendicular relation with said wire.
 8. An electricalcontrol device as defined in claim 6, wherein said linking member isthermally insulated from said conductive wire.
 9. An electrical controldevice as defined in claim 6, wherein said means for connecting saidwire to said other contact comprises a lever pivotally mounted toprovide a shorter length portion and a longer length portion, the outerend of said longer length portion being disposed to engage said othercontact, spring means to urge said other contact and said outer end ofsaid longer portion to move away from said one contact and saidconductive wire being secured between a fixed point and the outer end ofsaid shorter end portion, whereby small dimensional excursions of saidconductive wire cause said other contact to move a relatively largedistance in direct proportion to the ratio of the longitudinaldimensions of said shorter length portion to said longer length portion.10. An electrical control device as defined in claim 9, wherein the endsof said conductive wire are fixedly mounted in juxtaposition and theapproximate mid-point of said wire is secured to said outer end of theshorter length portion and is located equidistant from said ends of saidconductive wire.